Magnetic excitations in the S=1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature

Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in S = 1/2 dimermagnets, as revealed by the unusual asymmetric line shape of their excitations at finite temperatures. Here, we quantitatively explore and parametrize the strongly correlated magnetic excitations at finite temperatures using high-resolution inelastic neutron scattering of the model compound BaCu2V2O8 which we show to be an alternating antiferromagnetic-ferromagnetic spin-1/2 chain. Comparison to state of the art computational techniques shows excellent agreement over a wide temperature range. Our findings hence demonstrate the possibility to quantitatively predict coherent behavior at elevated temperatures in quantum magnets.